In the case of the production of frames for inlays, crowns and bridges, processes are known which replace the previous metal cast frame with a frame of spinel, alumina or metal powder. Such a process, which uses spinel or alumina as material, is known under the name VITA In-Ceram.RTM.. Another process, in which metal powder is used, is known under the name DEGUSSA-Degusint.RTM.. Both processes consist of the following important steps:
a) From the model is produced a double, usually of silicone mass. PA1 b) This double is poured out with a special gypsum and, after about 2 hours, a working model is removed from the mold. PA1 c) The working model is dry ground, the preparation limit marked, and, in the case of In-Ceram, a sealant is applied, whereby, on the other hand, in the case of Degusint, a bonding agent is used. PA1 d) In the case of Degusint, the working model is dried for 5 min at 700.degree. C., subsequently preheated at 700.degree. C. for 5 min, thereafter heated to 1100.degree. C., and calcined for 2 min. PA1 e) Slip or metal powder is applied to the sealed working model. PA1 f) In the case of In-Ceram, the working model is usually kept for 6 hours at 120.degree. C. and then heated to 1120.degree. C. over 2 hours and kept for 2 hours. PA1 g) After cooling, the In-Ceram is easily r(moved from the hollow space of the frame because of the gypsum shrinkage. PA1 h) Thereafter follows the infiltration of the frame with glass powder, the calcining of the frame, and the usual finishing of the frame, such as grinding off of the edges, sand blasting and again calcining. PA1 i) In the case of Degusint, the modelled tooth replacement is preheated to 700.degree. C. in a graphite box for 10 min in an open oven chamber and thereafter sintered for 15 min at a temperature of 1090.degree. C. (Degusint U) or 975.degree. C. (Degusint G). After expiration of the sinter time, the graphite box is transferred immediately and without interruption into the vacuum box; the cooling time amounts to at least 15 min.
From the above description, it can be seen that this process is very time-and labor intensive. The expenditure of time for a frame amounts, in the case of the In-Ceram process, to about 14 hours and, in the case of Degusint, to about 4 hours.